Electrodeposition of nickel

ABSTRACT

A WATTS BRIGHT NICKEL ELECTROPLATING BATH CONSISTING OF FROM 0.1 TO 1 G./L. OF A MIXTURE OF ACETYLENIC COMPOUNDS INCLUDING BOTH AN A-HYDROXY-ACETYLENIC COMPOUND AND AN ALKYLENE OXIDE CONDENSATION PRODUCT OF AN A-HYDROXY-ACETYLENIC COMPOUND IN A WEIGHT RATIO OF THE SAID CONDENSATION PRODUCT TO THE A-HYDROXY-ACETYLENIC COMPOUNDS OF FROM 1.5:1 TO 7:1, AND 0.2 OR 0.5 G./L. OR SACCHARIN.

US. Cl. 204-49 15 Claims ABSTRACT OF THE DISCLOSURE A Watts bright nickel electroplating bath consisting of from 0.1 to 1 g./l. of a mixture of acetylenic compounds including both an m-hydroxy-acetylenic compound and an alkylene oxide condensation product of an a-hydroxy-acetylenic compound in a weight ratio of the said'condensation product to the a-hydroxy-acetylenic compounds of from 1.5 :1 to 7:1, and 0.2 or 0.5 g./l. of saccharin.

This application is a continuation-in-part application of co-pending application Ser. No. 108,210, filed Jan. 20, 1971, now US. Pat. No. 3,711,384. Said application Ser. No. 108,210 discloses and claims aqueous nickel electroplating electrolytes of the Watts type and also of the high chloride type, containing from 0.1 to 1 g./l. of the mixture of acetylenic compounds specified hereinafter, and also containing from 1.0 to 5.0 g./l. of saccharin.

This invention relates to improvements in the electrodeposition of nickel, particularly to obtain bright electrodeposits.

It has long been known to employ various acetylenic compounds as organic brightening agents in nickel electroplating solutions. When an organic sulpho-oxygen compound is also present assertions have been made that a bright electrodeposit of nickel can be obtained from the solution. Thus in British patent specification No. 747,908 there is described the use as brightening additives in nickel electroplating solutions of certain acetylenic alcohols, particularly 2-butyn-1,4-diol, in combination with an organic sulpho-oxygen compound to obtain bright electrodeposits. Subsequently in British patent specification No. 864,287 the use in nickel electroplating solutions of alkynolepoxide adducts in conjunction with an organic sulpho oxygen comp ound was described as resulting in the formation of very bright nickel deposits. In both these specifications a wide variety of organic sulpho-oxygen compounds is mentioned as being suitable for use in combination with the particular acetylenic compounds specified and the use of naphthalene 1,3,6-trisulphonic acid is especially advocated.

' The compositions described in the aforesaid specifications are described with particular reference to the Watts bath, that is to an electrolyte comprising dissolved nickel-II sulphate (225-350 grams/litre), nickel-II chloride (30-50 grams/litre) and boric acid (20-45 grams/ litre). However, in such compositions the use of naphthalene trisulphonic acid (sodium salt) with 2-butyn- 1,4-diol or with the adduct of 2-butyn-l,4-diol with two moles of ethylene oxide [often termed 1,4-di-(fi-hydroxyethoxy)-2-butyl] gives only moderately satisfactory bright nickel electrodeposits due to poor levelling.

We have now discovered that much more satisfactory bright and level nickel electrodeposits can be obtained from a Watts" nickel electroplating bath if a particular combination of acetylenic brightening agents is employed in conjunction with particular amount of a particular ice type of sulpho-oxygen compound. The particular acetylenic addition agents involved are a mixture containing specified proportions of an a-hydroxyacetylenic compound and an alkylene oxide condensation product of such a compound and our discovery also involves the use of such mixture in conjunction with a concentration of from 0.2 to 5 gram/litre of saccharin. The use of saccharin gives electrodeposits with good ductility and with little tendency to undergo spontaneous cracking.

Accordingly, the present invention provides an aqueous electrolyte for nickel plating comprising (a) from 0 to gram/ litre of nickel-II chloride and nickel-II sulphate in an amount greater than the nickel-II chloride and up to 400 g./l., the total of nickel-ll chloride and sulphate being greater than g./l. (b) 0.1-1.0 gram per litre of a mixture of acetylenic compounds consisting of an a-hydroxy-acetylenic compound and an alkylene oxide condensation product of an a-hydroxy acetylenic compound in a weight ratio of the said condensation products to the u-hydroxy-acetylenic compounds of from 1.5:1 to 7:1; and (c) from 0.2 to 5.0 grams per litre of saccharin.

The invention is applicable to nickel plating electrolytes which comprise at least 150 grams per litre of a nickel- II chloride and sulphate combined. Such electrolytes are of the Watts type which comprise a major proportion, e.g. 100 to 400 and preferably 225-350 grams/litre of nickel-II sulphate, a minor proportion, e.g. 0 to 100 preferably 25 to 75, most preferably 30-50 grams/litre of nickel-Il chloride and typically 20-45 grams/litre of boric acid.

The ot-hydroxy-acetylenic compounds employed are compounds having a hydroxy group in an tat-position to an acetylenic linkage. Preferably such compounds are a-alkynols of the general formula RyCHOH-CzCR where R, and R are each hydrogen or an alkyl, alkenyl or alkynol group of l to 4 carbon atoms which may optionally contain an amino or hydroxyl substituent. Representative of such ot-alkynols include:

2-butyn-1,4-diol;

l-butyn-3-ol; propargyl alcohol (2-propyn-1-ol); 1-pentyn-3-ol; 4-methoxy-2-butyn-l-ol; 3-hexyn-2,5-diol; 4-diethylamino-2-butyn-l-ol; and 2,4-hexadiyn-1,6-diol The first three compounds of this list are especially useful.

The alkylene oxide condensation products of a-hydroxyacetylenic compounds for present use are formed by reacting an alkynol with from 1 to 20 moles, preferably l-4 moles, of an alkylene oxide. The preferred alkylene oxide is ethylene oxide, but propylene oxide, epichlorhydrin or epibromhydrin may also be used. Mixtures of such alkylene oxides may also be employed, either concurrently or consecutively, in the condensation with the ot-alkynol. The tit-alkynol may be a compound of the formula R1.CHOH.CECR2 as hereinbefore specified and particularly it is a member of the aforesaid list. The condensation product is formed by any of the methods usually employed for the formation of polyoxyalkylene ether from condensation of an alcohol with an alkylene oxide. The preferred condensation products are formed from 2-butyn-1,4-diol, 1-butyn-3-ol or propargyl alcohol with about 2 moles of ethylene oxide.

The above mentioned acetylenic compounds are employed in the electrolytes of the invention in a total concentration of 0.1 to 1.0 gram per litre. A greater weight of the a-alkynol/alkylene oxide condensation product is used over that of the simple a-alkynol, the weight ratio of vcondensatezot-alkynol being from 1.5 :1 to 7:1. Preferably,

the said ratio employed is from 2:1 to 55:1 since with the higher ratios there is a tendency to pitted deposits whilst with the ratio below 2011 the levelling action of the additive may become impaired.

The electrolyte is essentially free from other acetylenic compounds such as acetylenic sulphonates, which are ineffective and tend to increase the cost of the composition without improving the brightness.

The electrolytes of the invention comprise from 0.2 to 5 grams of saccharin. As is known in the art in connection with the use of saccharin as an additive to nickel plating baths, substituted saccharin compounds i.e. o-carboxybenzsulphimide which contains a nuclear substituent, for example an alkyl, haloor sulpho-substituent are equivalents of saccharin for this purpose. Similarly these substituted saccharins may be used in place of saccharin in the baths and processes of the present invention and are included within the scope of the term saccharin. For present purposes a concentration of 0.5 to 2.5 grams per litre of saccharin is preferred.

No other sulpho-oxygen compound is essential in the electrolytes of the invention, but the presence of an additional organic sulpho-oxygen compound is often advantageous in that the electrolyte often then exhibits an increased tolerance to changes during production plating conditions. Such sulpho-oxygen compound may be any that has hitherto been advocated for use in nickel electroplating as a carrier brightener, but naphthalene 1,3,6- trisulphonic acid (added as such or as its sodium salt) is normally preferred. Other organic sulpho-oxygen compounds which may be particularly mentioned in this connection include sodium alkyl sulphonate, sodium benzene sulphonate, benzene sulphonamide and p-toluenesulphonamide. Such additional organic sulpho-oxygen compound may be added in the amounts in which they are conventionally employed, e.g. from 2-20 grams/litre for aromatic sulphonates and from 0.5-3 grams/litre for sulphonamides. If the amount of saccharin is less than 0.5 grams/litre then the presence of additional sulpho-oxygen compounds is especially desirable.

The operating conditions for the present electrolytes are generally those normally employed for electrolytes based on the specified salts of nickel. In general the pH of the electrolyte should be between 2.5 and 5.5, a pH of 3.5-5.0 being preferred, and the temperature thereof should be 4070 C., an operating temperature of 50-60 C. being preferred. The electrolyte may be operated under a wide range of current densities, for example at from 2-100 amps/sq. ft. and the workpiece as cathode may be agitated in the electrolyte during operation or the electrolyte may be agitated, for example by blowing air therethrough.

The nickel electrodeposits of the invention may find use as such or as the base layer onto which chromium is subsequently electrodeposited.

EXAMPLE 1 The invention is illustrated by the following examples:

To a Watts electrolyte containing nickel sulphate (25,0 g./l.), nickel chloride (50 g./l.) and boric acid (40 g./l.) there was added:

Condensate of 2-butyn-1,4-diol (1 mol.) and ethylene oxide (2 moles) 0.175 2-butyn-1,4-diol 0.089 Saccharin 2.5 Naphthalene trisulphonic acid (sodium salt) 5.0

in British standard specification 1134). A similar degree of levelling was obtained when the naphthalenetrisulphonic acid was omitted.

EXAMPLE 2 Example 1 was repeated but with varying amounts of the two acetylenic compounds. The total acetylenic content was increased by up to 50% whilst keeping the ratio of condensate: a-alkynol constant. The degree of levelling remained at 70-75%, though there was a slight deterioration in the ductility of the deposit.

EXAMPLE 3 Example 1 was repeated but with the concentration of the condensate being 0.275 g./l. and that of 2-butyn- 1,4-diol being 0.05 g./l. With the use of the two acetylenic compounds in this weight ratio of 5.5 :1, the degree of levelling remained about 70%. There was a slight tendency for the production of pitted deposits, but this disappeared when the said ratio was reduced to 4:1.

EXAMPLE 4 Electrolytes were prepared according to Example 1 but with various amounts of saccharin. Excellent results were achieved down to a saccharin content of 0.5 g./l. However the brighteness deteriorated when the saccharin was reduced below about 0.2 g./l.

EXAMPLE 5 The electrolyte of Example 1 was tested in comparison with similar electrolytes containing 2-butyn-1,4-diol or its ethylene oxide condensate separately as sole brightener, in varying concentrations.

The maximum levelling which could be achieved with 1-butyn-2,4-diol alone was 40% compared with 70-75% in Example 1. The ethylene oxide condensate alone gave levelling up to 50%, but any attempt to improve upon this figure resulted in defective plating.

This example demonstrates the surprising synergism obtained in accordance with our invention by using mixtures of a-alkynol and ethoxy a-alkynol.

EXAMPLE 6 The electrolyte of Example 1 was compared with a previously proposed electrolyte containing as brightener:

Benzene sulphonamide Saccharin Sodium benzene sulphonate 4.5 Butynediol monosulphonate 0.32 Ethoxybutyn diol 0.325

In a prolonged series of trials it was observed that the comparative electrolyte initially gave discolored deposits at low current densities together with a tendency for pitting and difficulties in subsequent chromium plating.

The electrolyte of Example 1 provided improved deposits which showed no tendency for discoloration, reduced pitting and improved acceptance of chromium. It also gave more consistant results, indicating a greater tolerance of impurities. It was cheaper, more effective and more reliable.

We claim:

1. An acidic aqueous electrolyte for nickel electroplating comprising water and (a) from -400 grams per litre of nickel-II sulphate,

from 25-75 grams per litre of nickel-II chloride and from 20-45 grams per litre of boric acid;

(b) about 0.5 gram per litre of saccharin; and

(c) from 0.l-l.0 gram per litre of a mixture of acetylenic compounds consisting of (i)an a-hydroxy-acetylenic compound of the formula RICHOCHECRZ wherein R and R are each selected from hydrogen, and alkyl, alkenyl and alkynol groups having 1 to 4 carbon atoms; and (ii) a condensate of an u-hydroxyacetylenic compound having the aforesaid formula with from 1 to 20 moles of an alkylene oxide, in a weight ratio of said condensate to said a-hydroxyacetylenic compound of from 1.5 :1 to 7: 1.

2. An aqueous acidic electrolyte as claimed in claim 1 wherein said u-hydroxy-acetylenic compound is selected from the group consisting of 2-butyn-1,4-diol, 1-butyn-3-ol, propargyl alcohol, l-pentyn-3-ol, methoxy-Z-butyn-l-ol 3-hexyn-2,5 diol, 4-diethylamino-2-butyn-l-ol, and 2,4- hexadiyn-l,6-diol.

3. An aqueous acidic electrolyte as claimed in claim 2 wherein said alkylene oxide is selected from the group consisting of ethylene oxide, propylene oxide, epichlorhydrin and epibromhydrin.

4. An electrolyte according to claim 3 wherein contains a second organic sulpho-oxygen compound.

5. An electrolyte according to claim 4, containing naphthalene-1,3,6-trisulphonic acid or a salt thereof.

6. An electrolyte according to claim 3 comprising from 225-350 grams per litre of nickel-II sulphate, from 30- 50 grams per litre of nickel-II chloride and from 20-45 grams per litre of boric acid.

7. An electrolyte according to claim 1 wherein the weight ratio of the said condensate to the said OL-hYdIOXY- acetylenic compound is within the range of 2:1 to 5.5:1.

8. An electrolyte according to claim 7 wherein said ahydroxy acetylenic compound is 2- butyn-1,4-diol, and said condensate is a condensate of 2-butyn-1,4-diol with from 1 to 4 moles of ethylene oxide.

9. An electrolyte according to claim 1 wherein the said alkylene oxide condensate contains from 1 to 4 oxyethylene units.

10. An electrolyte according to claim 1 wherein the said alkylene oxide condensate is a condensate of 2-butyn-1,4' diol with ethylene oxide.

11. An electrolyte according to claim 1 wherein the ahydroxyacetylenic compound present is 2-butyn-1,4-diol.

12. A nickel plating electrolyte according to claim 1 comprising from 225 to 350 g./l. of nickel-II sulphate, from 30 to 50 g./l. of nickel-II chloride, 20 to 45 g./l. of boric acid, 0.1 to 1.0 g./l. total content acetylenic compounds, about 0.5 g./l. saccharin and from 2 to 20 g./l.

of aromatic sulphonate, said acetylenic compounds consisting of 2-butyn-1,4-diol and a condensate thereof with from 1 to 4 moles of ethylene oxide, in a relative weight proportion of from 1:15 to 1:7.

13. An aqueous acidic electrolyte as claimed in claim 1 having a pH of between 2.5 and 5.5.

14. An acidic aqueous electrolyte for nickel electroplating comprising water and (a) from 100-400 grams per litre of nickel-II sulphate, from 25-75 grams per litre of nickel-II chloride and from 20-45 grams per litre of boric acid; (b) about 0.2 gram per litre of saccharin; and (c) from 0.1-1.0 gram per litre of a mixture of acetylenic compound consisting of (i) an a-hydroxyacetylenic compound of the formula wherein R and R are each selected from hydrogen, and alkyl, alkenyl and alkynol groups having 1 to 4 carbon atoms; and (ii) a condensate of an a-hYdIOXY- acetylenic compound having the aforesaid formula with from 1 to 20 moles of an alkylene oxide, in a weight ratio of said condensate to said a-hydroxyacetylenic compound of from 1.521 to 7: 1.

15. A nickel plating electrolyte according to claim 14 comprising from 225 to 350 g./l. of nickel-II chloride, 20 to g./l. of boric acid, 0.1 to 1.0 g./l. total content acetylenic compounds, about 0.2 g./l. saccharin and from 2 to 20 g./l. of aromatic sulphonate, said acetylenic compounds consisting of 2-butyn-l,4-diol and a condensate thereof with from 1 to 4 moles of ethylene oxide, in a.

relative weight proportion of from 1:1.5 to 1:7.

References Cited UNITED STATES PATENTS 3,366,557 1/ 1968 Foulke et al 204-49 3,574,067 4/1971 Spiro 204-49 X 3,630,857 12/ 1971 DuRose et a1. 204-49 GERALD L. KAPLAN, Primary Examiner 

